Bump pyyaml from 3.11 to 5.1 in /scripts

Bumps [pyyaml](https://github.com/yaml/pyyaml) from 3.11 to 5.1.
- [Release notes](https://github.com/yaml/pyyaml/releases)
- [Changelog](https://github.com/yaml/pyyaml/blob/master/CHANGES)
- [Commits](https://github.com/yaml/pyyaml/compare/3.11...5.1)

Signed-off-by: dependabot[bot] <support@github.com>

scripts/requirements-simple.txt

@@ -1,4 +1,4 @@
 requests==2.9.1
 six==1.10.0
-PyYAML==3.11
+PyYAML==5.1
 ujson==1.33

scripts/requirements.txt

@@ -1,7 +1,7 @@
 boto3==1.4.0
 botocore==1.4.53
 Fiona==1.6.3.post1
-PyYAML==3.11
+PyYAML==5.1
 Rtree==0.8.2
 Shapely==1.5.14
 Unidecode==0.4.19